The invention relates generally to electromagnetic clutch assemblies for transfer cases and the like and more specifically to a transfer case clutch assembly wherein a clutch pack assembly having an ancillary locking clutch and an electromagnetic operator are disposed on opposite sides of a chain drive sprocket.
Contemporary transfer case clutches represent numerous engineering and operational approaches. A fundamental distinction between many of these approaches is whether the operator is hydraulically or electrically powered. Hydraulically operated clutches are disclosed in, for example, U.S. Pat. No. 4,846,298 to Naito, 5,002,147 to Tezuka, et al. and U.S. Pat. No. 5,010,974 to Matsuda. Electric or electromagnetic clutch operators are disclosed in, for example, U.S. Pat. Nos. 4,718,303, 5,407,024 and 5,584,776. These patents all disclose various transfer case, clutch and control configurations adapted to provide performance which addresses various operational parameters. Other configurations address other operational features and parameters.
As the designs and configurations for transfer case clutches have progressed, certain operational features and parameters have increased in importance and others have decreased. One such feature of increasing importance is the capability to couple or lock the primary drive line and the secondary drive line through the transfer case. In extreme operating conditions, particularly in low gear, direct, i.e., non-modulated, equal torque delivery to the primary and secondary drive lines provides desirable and predictable control, driveability and traction. Such a coupling or locking device also allows the modulating clutch and actuator to be de-energized, reducing wear and heat generation in the transfer case during operating conditions where both could be significant.
A relatively constant goal over time has been improved fuel economy. Within the context of transfer cases, improved fuel economy involves reduction of drag, primarily in two-wheel drive operation by reducing any frictional coupling between the operating and non-operating components. The present invention is directed to both of these goals.